Studies proposed will test several hypotheses concerning the mechanism of human cataract formation. 1) Age-related nuclear cataracts may occur when the normal barriers that maintain low oxygen concentration in the lens are compromised. To test this possibility a bioassay to measure [O2] in the lens will be validated. This assay will then be used to determine whether lens [O2] is increased in cataract patients, including patients who develop cataracts after vitrectomy. 2) We found that the lens expresses components of the "hypoxia response system." Whether this regulatory system is responsible for the atypical metabolic characteristics of the lens and whether treatment with hyperbaric oxygen alters the levels of hypoxia-induced enzymes and growth factors in the lens will be determined. These studies have the potential to transform our understanding of lens metabolism and growth. 3) We adapted a method to detect somatic mutations in lens epithelial cells. 4) Hydrogen peroxide in the aqueous humor has been suggested as a risk factor for human cataracts. We will evaluate H2O2 levels in the aqueous humor of patients with clear lenses and cataracts and determine the source(s) of peroxide in the eye. 5) One source of increased oxygen in the aging eye may be increased circulation of vitreous humor following liquefaction of the vitreous body. We will develop methods to measure vitreous liquefaction and correlate it with the onset of nuclear cataracts. We identified an active VEGF signaling system in adult and embryonic lenses and will determine the importance of this pathway in lens development, growth, and function by creating mice that do not express the VEGF receptor in the lens. We also isolated two new transcripts that are expressed at the latest stage of lens fiber cell maturation. The function of the proteins they encode and the factors responsible for regulating these genes will be determined. Mice in which one of these genes has been deleted are being produced and we developed the means to express these proteins at early stages of lens fiber formation. These experiments will allow the determination of the function and distribution of these proteins in the lens in vivo.